Since conventional piano actions for upright pianos do not provide the same interpretation possibilities as grand piano actions do, attempts have been made to adapt onto upright pianos, actions which are derived from those of grand pianos, as taught for example in British Pat. No. GB 226 616.
Until now, however, there has been no successful attempt to design damper mechanisms for upright pianos which provide all the advantages of the damper mechanisms used in grand pianos, i.e.
actuation by the key itself
return by gravity, without springs
displacement exactly perpendicular to the strings
arrangement on support bars fully independent from the keys and from the hammer mechanism, and moreover, these mechanisms should be accommodated within the space between the hammer mechanisms and the strings.
Only document DE 97 885 proposes a solution bringing certain of the aforesaid advantages:
actuation by the key itself
return by gravity, without springs
accommodation of the mechanisms within the space between the hammer mechanisms and the strings but the displacement of the damper blocks follows an arc of circle, and is not exactly perpendicular to the strings.